fix(web): handle real signup errors on register (no more false success)

better-auth's signUp.email returns { error } instead of throwing (same as
login.tsx), so the old try/catch never caught auth failures: a failed signup
still showed "Hesap oluşturuldu!", fired user_signed_up / CompleteRegistration,
and redirected to the dashboard. Now we check the returned error, distinguish
"e-posta zaten kayıtlı" (via /users/check-email) from other failures (showing
the actual reason, e.g. weak password), keep the user on the form, and only
fire success analytics on real success. Network failures get a distinct
"Bağlantı hatası" toast.

Also: CTA "Kayıt Ol" -> "Ücretsiz Başla" (matches pricing) and added
"Spam göndermeyiz" trust microcopy.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

apps/web/src/routes/_auth/register.tsx

@@ -1,3 +1,4 @@
+import { api } from "@/lib/api-client";
 import { signIn, signUp } from "@/lib/auth-client";
 import { startAction } from "@/lib/faro";
 import { track as trackMeta } from "@/lib/meta-pixel";
@@ -40,16 +41,40 @@ function RegisterPage() {
     setLoading(true);
 
     try {
-      await signUp.email({ name, email, password, callbackURL: redirectUrl });
-      capture("user_signed_up", { method: "email" });
-      trackMeta("CompleteRegistration", { method: "email" });
+      // better-auth returns { error } rather than throwing (see login.tsx).
+      // The old code awaited without checking error, so failed signups still
+      // reported success, fired user_signed_up, and redirected to the dashboard.
+      const { error } = await signUp.email({ name, email, password, callbackURL: redirectUrl });
+
+      if (error) {
+        let exists = false;
+        try {
+          ({ exists } = await api.post<{ exists: boolean }>("/users/check-email", { email }));
+        } catch {
+          // fall through to a generic message
+        }
+        if (exists) {
+          toast.error("Bu e-posta zaten kayıtlı", {
+            description: "Bunun yerine giriş yapmayı deneyin.",
+          });
+        } else {
+          toast.error("Kayıt başarısız", {
+            description:
+              error.message ?? "Şifre en az 8 karakter, 1 büyük harf ve 1 rakam içermelidir.",
+          });
+        }
+        return;
+      }
+
       // The referral code travels via `?ref=` in redirectUrl; the welcome
       // onboarding modal on the search page is the single place that applies it
       // (covers both email and Google OAuth signups).
+      capture("user_signed_up", { method: "email" });
+      trackMeta("CompleteRegistration", { method: "email" });
       toast.success("Hesap oluşturuldu!");
       window.location.href = redirectUrl;
     } catch {
-      toast.error("Kayıt başarısız. Bu e-posta zaten kullanılıyor olabilir.");
+      toast.error("Bağlantı hatası", { description: "Lütfen tekrar deneyin." });
     } finally {
       setLoading(false);
     }
@@ -163,12 +188,12 @@ function RegisterPage() {
           />
         </div>
         <Button type="submit" className="w-full" disabled={loading}>
-          {loading ? "Kayıt yapılıyor..." : "Kayıt Ol"}
+          {loading ? "Kayıt yapılıyor..." : "Ücretsiz Başla"}
         </Button>
       </form>
 
       <p className="text-center text-xs text-muted-foreground">
-        Kayıt olunca hemen VIN aramaya başlayın
+        Kayıt olunca hemen VIN aramaya başlarsın · Spam göndermeyiz
       </p>
 
       <p className="text-center text-sm">